1. Field of the Invention
The present invention relates to a workpiece changing system for changing workpieces for machining by a machine tool, etc., using a robot for handling a workpiece.
2. Description of the Related Art
As a method of mounting an un-machined workpiece or a partly machined workpiece on a jig, there is known a method in which male screws are inserted into female screws formed on the workpiece from behind of the jig and brought into engagement with the female screws to fix the workpiece on the jig by threaded engagement of the screws. Since positions of the female screws formed on a workpiece are different depending on a kind of product to be obtained, the mounting of a workpiece on the jig has to be performed manually and thus it has been hardly possible to change a workpiece by a robot.
Further, in the case of handling a heavy workpiece by a robot, large moment is applied to joint axes of a robot wrist when the robot wrist changes its orientation. Since load capability of the joint axes of the robot wrist is relatively small with respect to the joint axes of the other parts of the robot, it is not desirable to change orientation of the robot wrist with the heavy workpiece held thereon. It has been required to change the orientation of the robot wrist in mounting and dismounting a workpiece on the jig by a robot, and therefore it has been difficult to adopt a robot for changing the heavy workpiece on the jig.
An object of the present invention is to enable automatic attaching and detaching of a heavy workpiece on a jig using a robot. Further, the present invention enables automatic clamping and unclamping of a workpiece on a jig by a robot to realize a full automatic operation of changing workpieces.
A workpiece changing system of the present invention is for attaching a workpiece to be machined on a jig and/or detaching a machined workpiece from the jig by holding the workpiece with a robot hand attached to a handling robot, and comprises: a jig mounting device including a mounting unit on which the jig is mounted; fixing means for fixing the jig on the mounting unit; and orientation changing means for changing an orientation of the jig on the mounting unit so that an orientation of the jig conforms with an orientation of the workpiece held or to be held by the robot hand in attaching/detaching of the workpiece on/from the jig. The orientation changing means may comprise rotating means for rotating the jig mounting unit and tilting means for tilting the jig mounting unit.
The workpiece changing system may further comprise: a pull bolt attaching/detaching robot having a pull bolt attaching/detaching device for attaching/detaching pull bolts on/from the workpiece by threaded engagement with threaded holes formed on the workpiece, the workpiece with the pull bolts attached being positioned on the jig by the handling robot, a pulling hydraulic cylinder device with a position arranged at said jig; a ball lock mechanism connected to the piston of the pulling hydraulic cylinder device for locking a distal end of the pull bolt, whereby the workpiece is fixed and positioned on the jig by a hydraulic pulling force of the piston. Thus, the attachment/detachment of the workpiece on/from the jig is automatically performed. The pull bolt attaching/detaching device may comprise a holding mechanism for holding a pull bolt, an engaging member to be engaged with the pull bolt held by said holding mechanism so as to transmit a rotational torque to the pull bolt, and a pushing mechanism for pushing the engaging member to be engaged with the pull bolt.
The workpiece changing system of the present invention may further comprise an automatic storehouse for storing workpieces to be machined and machined workpieces, and in this case the handling robot may handle a workpiece to be machined taken out from the storehouse to attach the workpiece on the jig mounted on the jig mounting device, and handle the machined workpiece to detach the machined workpiece from the jig mounted on the jig mounting device and transfer the machined workpiece to the automatic storehouse to be automatically stored therein. Also, the handling robot may handle a workpiece to be machined taken out from the storehouse to attach the workpiece on the jig mounted on the jig mounting device in cooperation with the pull bolt attaching/detaching robot.